This invention relates to methods of forming conductive lines, insulative spacers over conductive line sidewalls, and memory circuitry.
Fabrication of integrated circuitry involves the formation of conductive lines over a substrate. Such conductive lines are used to connect to or with device components. One type of integrated circuitry is memory circuitry. Memory circuitry typically includes a memory array in which storage devices are fabricated as close as lithography allows in order to conserve wafer space. Memory circuitry also typically includes peripheral circuitry in which spacing requirements are not as paramount as in the memory array. Accordingly, devices in the peripheral circuitry are typically spaced further apart relative to devices in the memory array.
The disparity in spacing between conductive lines in the memory array relative to those lines in the peripheral area leads to a problem which this invention addresses. Specifically, conductive lines typically include sidewall spacers which electrically insulate sides of the conductive lines. The sidewall spacers are typically formed by forming a layer of insulative material over the substrate and anisotropically etching the layer to leave spacers about the conductive lines.
It is well known that the conformality of deposited insulative material over closely spaced conductive lines is worse than on lines which are spaced further apart. Because of this, peripheral devices tend to have larger dimensioned spacers than array devices. Such larger dimensions typically manifest in larger lateral spacer width dimensions. Because the spacer dimension is typically set by the processing required to optimize devices in the memory array, the peripheral devices can be compromised by having larger spacers than would be the case if the spacers were optimized for the peripheral devices. Larger dimensioned spacers adversely affect electrical properties associated with the lines and degrade device performance. Device reliability may also suffer if lightly doped drain regions are not used. Such is typically the case in some low Vcc processes.
This invention arose out of concerns associated with providing methods to enhance the performance of peripheral devices without compromising the performance of the array devices.
Methods of forming conductive lines and insulative spacers thereover are described. In accordance with one aspect of the invention, a substrate is provided having a first area and a second area relative to which conductive lines are to be formed. A layer of conductive material is formed over the first and second substrate areas and a layer of insulative material is formed over the conductive material. In a preferred implementation, insulative material is removed from the second area and conductive lines are subsequently patterned and etched in both the first and second areas. In another preferred implementation, conductive lines are first patterned and etched with insulative material in the second area being subsequently removed. The patterned and etched conducted lines have respective sidewalls. Subsequently, a layer of insulative material is formed over the substrate, the conductive lines, and the respective sidewalls thereof, and in at least one common etching step, the insulative material is etched to a degree sufficient to form sidewall spacers over the respective sidewalls. In accordance with one aspect, the one common etching step comprises an anisotropic etching step. In accordance with another aspect, the one common etching step comprises at least one facet etching step.